The present invention relates to a pneumatic tire having an improved carcass line which is capable of reducing the transmission of vibration during running and thereby reducing road noise.
Tires vibrate during running caused by roughness of the road surface, and the vibrations are transmitted from the tire tread portion to the vehicle body through the tire sidewall and bead portions and the wheel to produce the so called road noise which has a peak which lies around 200-250 Hz. In a radial tire provided with a stiff belt, e.g. a steel belt, the road noise is remarkably large. Therefore, in order to reduce the road noise, the tread rigidity has been decreased by decreasing the tread rubber hardness and/or belt cord modulus. Further, it has been proposed to provide the inside of the tire with a vibration damper layer made of a foam rubber.
However, when the tread rigidity is lowered, the cornering force is inevitably decreased, causing a deterioration in the steering performance. On the other hand, when a damper layer is disposed in the tire, the dynamic balance of the tire is disturbed, and the ride comfort deteriorates.
It is therefore an object of the present invention to provide a pneumatic tire in which, the road noise can be reduced without lowering the tread rigidity and without using an additional damper material.